The invention relates to a leakage oil return apparatus for a hydraulic motor for returning the oil leaked from the working pressure space of a motor into a motor casing from the casing back to a return line of the motor.
Pressures existing in the pressure and return lines of sizable hydraulic motors are comparatively high: on the delivery side e.g. 150-350 bar, and even on the return side higher than allowable casing pressures, often up to dozens of bar. Momentarily, even the return line pressure may rise to above 150 bar (e.g. as the running direction is reversed). With such high pressures, it is inevitable that internal leakage occur within a motor from the working pressure space of the motor into the motor casing. This leakage oil is exploited for lubrication duties, but excess oil must be expelled from the casing and returned to circulation. Motors use hydraulic oil for lubrication through lubricating conduits constructed from the delivery side to oiling points. For example, the lubrication of crankshaft and piston-pin bearings can be arranged with internal drain conduits from the delivery side, the motor consequently leaking also through the slide bearing packings of these conduits. For this reason, the sizable hydraulic motors are constructed with a separate drain line for carrying the leakage oil through a tank to circulation. Since the motor can be located at the end of long hoses, the construction of a separate drain line incurs extra costs, in addition to which the casing oils are generally delivered into the tank in unfiltered condition so as not to develop a back pressure in the drain line. The leakage oil carries impurities from the motor into the casing and thence along a drain line into the tank. This, in turn, results in a faster wear of the system, more breakdowns, and a shorter service life for the equipment.
It is an object of the invention to provide a leakage oil return apparatus for a hydraulic motor, which is not hampered by the above problems.
This object is achieved by the invention on the basis of the characterizing features set forth in the appended claim 1. The non-independent claims disclose preferred embodiments of the invention.